Hydrodynamics of a tropical estuary: Buranhém River, Porto Seguro, Brazil

Ana Carolina Rodrigues De Sá Silva,Arcilan Trevenzoli Assireu,Eduardo Siegle,Paulo Henrique Gomes De Oliveira Sousa,Dustin Brown,Marcos Eduardo Cordeiro Bernardes

doi:10.1590/2318-0331.0318170141

Abstract

ABSTRACT Estuaries are dynamic environments that are highly vulnerable to anthropogenic influences, especially when adjacent to urban areas. In this study it is assessed for the first time the hydrodynamic characteristics of the Buranhém estuary (Northeast Brazil). The aim is to define the salt transport mechanisms and the hydrodynamics and stratification patterns of this tropical estuary, under both spring and neap tidal conditions. Fieldwork was carried out during 8 days covering varying tidal range conditions (July 30th to August 7th, 2015). Salinity and temperature were continuously monitored at moored stations at both the surface and bottom, whereas velocity profile was sampled by a bottom-mounted instrument. Average velocity in the water column was 0.46 m.s-1 during flood tides and 1.0 m.s-1 during ebb tides. Residual currents were seaward, with ebb dominance. The dominant salt transport mechanism is turbulent diffusion. Most of the layer Richardson values did not exceed 2, indicating well mixed conditions mainly during spring tides. Stratification varies with tide condition, with spring tides being able to further mix the vertical structure. Vertical velocity gradients that generate vertical mixing overcome the stabilizing effects generated by vertical density gradients.

Highlights

Coastal zones and their associated environments are among the regions of highest population density in Brazil (IBGE, 2013), and high anthropogenic pressure increases the vulnerability of these areas
Estuaries are vulnerable to human activity, since they are used for access to the interior of the continent, they are receiving bodies for natural and industrial effluents, and they are subject to high human occupancy rates in their surroundings (MIRANDA et al, 2002; PEREIRA et al, 2010)
The spring tide period began on July 31st, 2015 and neap tide started on August 6th, 2015 (Figure 4)

Summary

Introduction

Coastal zones and their associated environments are among the regions of highest population density in Brazil (IBGE, 2013), and high anthropogenic pressure increases the vulnerability of these areas. One of such environments are estuaries, which are semi-enclosed bodies of water with an open connection to the ocean. There is mixture between continental freshwater and the saltwater provided by the adjacent ocean (CAMERON; PRITCHARD, 1963; PEREIRA et al, 2010) These environments provide a range of ecosystem services, such as the nurturing of life, coastal protection, purification of water, and carbon capture, among others. Estuaries are vulnerable to human activity, since they are used for access to the interior of the continent, they are receiving bodies for natural and industrial effluents, and they are subject to high human occupancy rates in their surroundings (MIRANDA et al, 2002; PEREIRA et al, 2010).

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